Replacing the ecm wouldn't be my first choice.
If your interested in GM ecm applications, here is a site.
www.cruzers.com/~ludis
When the site comes up click on the P4 link, scroll down the page, find your engine size and vin, go across the page to your year.
Like the other person said, the ecm number should be on the ecm.
I don't know how accurate the info is on that web-site, but it is interesting.